1. Field of the Invention
The present invention relates to bookbinding and its products such as files wherein a plurality of bound sheets which are superposed with each other are bonded to an inner face of a spine of a cover at arranged ends.
2. Prior Art
Conventional bookbinding was generally achieved by adhering the arranged ends of the bound sheets to the inner face of a cover using an adhesive. It is one problem of the prior art to require use of an adhesive and another problem that a cheap adhesive having excellent adhesive strength is difficult of obtain when the bound sheets and the cover are made with a thermoplastic resin such as polypropylene.
For solving these problems, there have been known bookbinding techniques wherein the arranged ends of bound sheets formed of a thermoplastic resin are bonded to the inner face of a spine made with the same thermoplastic resin by holding the arranged ends of the superposed bound sheets in a clamping means with a slight projection of the ends. Pressing the inner face of the spine onto the ends and using a high frequency vibrator such as a ultrasonic horn from the rear side of the spine of the cover thereby weld the thermoplastic resins of the ends of the bound sheets and the inner face of the spine.
Such welding bookbinding using a high frequency vibrator has the drawback that welding time is comparatively long and thereby increases power consumption. Furthermore, the outer face of the spine is likely to melt or suffer damage or breakage due to a successive pressing of the high frequency vibrator.